Rearrangements of the ALL-1/MLL1 gene, resulting in production of ALL-1 fusion proteins, underlie the vast[unreadable] majority of infant acute leukemias and of a substantial part of a therapy-related leukemia. The way by which[unreadable] the fusion proteins trigger leukemia is not known. Here we attack this issue in several directions: 1) we have[unreadable] recently found that expression of ALL-1 fusion proteins in leukemic and transfected cells results in[unreadable] upregulation of a specific micro RNA. miR-191. We found that the upregulation is due to recruitment of ALL-1[unreadable] fusion proteins, together with the general processor of microRNAs-Drosha, to the miR-191 locus. Since[unreadable] Drosha is not recruited with normal ALL-1 to the same locus (nor was it shown to be bound to other rniR[unreadable] loci), we consider this recruitment as very significant in miR-191 upregulation. Included in the proposal are[unreadable] experiments concerning potential association between ALL-1 fusion proteins and Drosha, involvement of[unreadable] Drosha's recruitment in miR-191 overexpression in solid tumors, direct role of miR-191 in onset of acute[unreadable] leukemia, effect of miR-191 overexpression on differentiation of hematopoietic precursor cells, and[unreadable] identification of miR-191 target gene(s). 2) We have used a combination of conventional columnes,[unreadable] immunearflnlty purification, and mass spectrometry analysis to identify a series of proteins associated with[unreadable] ALL-1/AF4 within a multiprotein complex. The identified proteins will be examined by multiple approaches to[unreadable] determine whether they constitute integral components of the ALL-1/AF4 complex. A follow-up will focus on[unreadable] interesting components. 3) Following our success in bringing off a genome-wide location analysis of normal[unreadable] ALL-1, we will extend it to a global analysis of the gene targets of ALL-1 fusion proteins ALL-1/AF4 and ALLVAF9[unreadable] in leukemic lymphoid and myeloid cell lines, respectively.[unreadable]